It is well known to transmit digital representations of a multiplicity of conversations along a single transmission link by periodic sampling of an analog signal, such as a voice signal, and transmitting discrete digital samples in place of analog signals. The Nyquist sampling theorem fixes the minimum sampling rate as twice the highest frequency of the signal sampled analog.
One widely used technique for digital is PCM, i.e. pulse code modulation, whereby each sample is expressed in an 8 bit code. Various other types of coding for digital information transmission are also known and used. Most conventional digital transmission techniques are characterized in that only a single sample relating to a single conversation is transmitted at a given time. Therefore, using conventional technology, one can transmit 30 voice and 2 signaling channels over a single communications link.
There is described and claimed in applicant's Israel patent application 63117, which issued Dec. 20, 1984, an apparatus and method for transmitting digital information by encoding a plurality of signals coded into a multiplicity of digital code elements in accordance with a first modulation technique; and for generating and transmitting coded addresses, each encoded address represents a digital code in accordance with a second modulation technique corresponding to a combination of code elements of individual ones of the plurality of signals.
The present invention seeks to provide a method and apparatus for transmitting of voice signals which enables maximum benefit to be obtained from the technique of the aforesaid issued Israel patent application 63117. The technique and apparatus of the present invention is also applicable to transmission techniques other than that described in the aforesaid issued Isrel patent application 63117.